Stylasterids show a pronounced insular distribution pattern, being found primarily off small (less than 36,000 km') oceanic islands, atolls, and archipelagos, and on seamounts and submarine ridges. Although lowered salinity and increased sedimentation may exclude stylasterids from the coasts of larger continental land masses, it is more likely that the availability of hard substrate and the low nutrient levels associated with steep-sided oceanic islands favor the establishment of stylasterids. Azooxanthellate Scleractinia, another calcified cnidarian taxon, have a broader distribution than stylasterids because they are assumed to be better competitors: having a greater dispersal ability, better sediment-shedding ability, and the ability of some to live on soft substrates.